New Swine Flu Has Avian Flu Genes

Researchers have identified a new strain of swine
influenzaH2N3which belongs to the group of H2 influenza viruses
that last infected humans during the 1957 pandemic. This new strain has a
molecular twist: It is composed of avian and swine influenza genes.

The group studied an unknown pathogenfirst identified by
University of Minnesota veterinary
diagnostician Marie Gramerthat infected two groups of pigs at separate
production facilities in 2006. Both facilities used pond water frequented by
migrating waterfowl.

Molecular studies indicated the unknown pathogen was an H2N3 influenza
virus that is closely related to an H2N3 strain found in mallard ducks. But
this was the first time it had been observed in mammals.

Influenza viruses have eight gene segments, all of which can be
swapped between different virus strains. Two of these gene segments code for
virus surface proteins that help determine whether an influenza virus is able
to infect a specific host and start replicatingthe first step in the
onset of influenza infection.

In the newly isolated swine H2N3, the avian H2 and N3 gene segments
mixed with gene segments from common swine influenza viruses. This
exchangeand additional mutationsgave the H2N3 viruses the ability
to infect swine. Lab tests confirmed that this strain of H2N3 could also infect
mice and ferrets.

These findings provide further evidence that swine have the potential
to serve as a mixing vessel for influenza viruses carried by birds,
pigs and humans. It also supports the need to continue monitoring
swineand livestock workersfor H2-subtype viruses and other
influenza strains that might someday threaten swine and human health.